In filter assemblies, a filter cartridge is generally disposed within and secured to a housing. The filter cartridge is often secured to the housing by separate components, such as tie rods, or flanges and bolts, or the like. These separate components, however, result in added inventory and equipment expenses, as well as assembly costs.
The filter cartridge is typically tightly sealed to the housing at its inlet or outlet to preclude the bypassing of fluid or contaminants. Replacement of the filter cartridge may be accomplished by replacing the entire filter assembly in a housing that has been permanently closed, for example, by welding. Alternately, in assemblies where the housing is not permanently sealed, the filter may be removed from the housing for separate replacement or disposal.
Filter cartridges generally comprise a filter material and one or more end caps. Filter cartridge end caps are frequently constructed of polymeric materials, while housings are generally metal or the like. The filter cartridge is often sealed to the housing by means of an separate elastomeric material disposed between mating surfaces of the end cap and the housing. Such elastomeric seals are typically flat or O-ring gaskets disposed between annular surfaces of the end cap and the housing.
A number of disadvantages are associated with arrangements which utilize extraneous securing devices or gaskets, such elastomeric seals. For example, in order to accommodate piston-type O-ring seals, grooves or complex crevices must generally be molded or machined in the annular surface of the end cap. Similarly, where extraneous securing devices are utilized, the housing and/or the filter cartridge must be molded or machined to accommodate the extraneous devices. Manufacture of these components may require more complex tooling or additional operations, and, therefore, results in additional costs. Further, crevices in such designs often provide a dead volume that may be undesirable for filtration of ultrapure gas systems.
Additionally, elastomeric seals, and piston-type O-ring seals in particular, have a relatively low resistance to relative longitudinal motion of the mating parts. Relative motion between components can chafe the components and generate debris within the flow path. In more extreme situations, the filter may be forced off the mating housing fitting by reverse flow, or system "hammer." Consequently, the filter assembly often includes additional means for preventing longitudinal movement of the filter cartridge within the housing, as, for example, by a mechanical interlock.
Further, elastomeric materials are often subject to out-gassing under certain conditions. This phenomenon is particularly troublesome in high purity gas filtration, such as in the manufacture of electronic chips. In chip manufacture, the filter elements are typically constructed entirely of TEFLON.RTM. PFA. Consequently, it may be difficult to provide an effective seal between the filter end cap and the housing. Moreover, elastomeric seals, as well as extraneous securing devices, may be a source of contamination and potential chemical incompatibility.